Oscillator for centimeter waves



March 30, 1948. A. l||. TURNER OSCIILLATOR FOR CENTIMETER WAVES Filed Sept. 16, 1943 Patented Mar. 30,*1948 OSCILLATOR FOR CENTIMETER WAVES Alfred H. Turner, Collingswood, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application september 16, 194s, serial No. 502,702

1 10 Claims.

This invention relates generally to centimeter wave oscillators and more particularly to centimeter wave thermionic tube oscillators employing inductive feedback.

Because of the low values of inductance permissible in centimeter wave oscillators, it is usually difcult with standard thermiondc tubes to tap the cathode circuit effectively to the main tuning inductarrce at a suitable point intermediate the grid and anode connections. However, with tubes of the lighthouse type s'uch as the General Electric models GL-446 -and ZP-464, having extremely low internal inductances and capacitances, more freedom is permissible in shaping the external inductive circuit elements. With tubes of the type described, it-has been found practicable to provide a capacity tunedinductive feedback circuit for wavelengths as short as 11 centimeters at fundamental resonance and for shorter wavelengths when employing parasitic resonances.

The inductive feedback type of oscillator circuit has been found to be superior to the capacity feedback (Colpitts) circuit when relatively wide frequency tuning range isrequired, since the tuning affects the feedback less in the inductive feedback circuit. This condition is especially true when ya variable capacitor is provided for tuning the resonant circuit.

The inductive feedback type of oscillator circuit has also been found to be superior to the grounded grid type of oscillator since the latter requires two tuned circuits for effective frequency adjustment over any considerable operating wave band. Y

Among the objects of the invention are to provide an improved method of and means for generating oscillations at centimeter waves. Another object of the invention is to provide an improved vcentimeter wave thermionic tube oscillator employing inductive feedback. A further object of the invention is to provide an improved centimeter wave oscillator having inductive feedback and unitary frequency adjusting means.

Further objects o-f theinvention include an improved centimeter wave inductive element. Another object of the invention includes an improved centimeter wave reactive circuit component. A further object of the invention includes an improved centimeter wave oscillator having means for adjusting the frequency over a relatively wide frequency band. An additional object is to provide .an improved centimeter wave Y, adjustable frequency oscillator including means for modulating electromechanically the output frequency of said oscillator. A

The invention will be further described by reference to the yaccompanying drawing of which Figure 1 is an elevational cross-sectional view of one embodiment of the invention; Figure 2 isa schematic circuit diagram of the equivalent electrical circuit of Figure l; Figure 3 is a cross-sectional elevational view of a'second embodiment of the invention; Figure 4 is a schematic circuit diagram of the equivalent electrical circuit of Figure 3; Figure 5 is a cross-sectional elevational view of a third embodiment of the invention, and Figure 6 is a schematic circuit diagram of the equivalent electrical circuit of Figure 5. Similar reference characters are applied to similar elements throughout the drawing.

Referring to Figure 1, a thermionic tube 1 o f the lighthouse type such as, for example, the General Electric types G11-446 or Z13-464, includes a cathode element 2 which is coupled capacitively, as indicated by the dash lines, to an external cathode shell 3. A transverse grid element, disposed parallel to the electron emissive surface of the cathode 2 is terminated in a conductive grid contact ring 4 which is separated from the cathode shell 3 by means of an insulating sleeve 5. An anode electrode 6 is cylindrical in shape, Iand is terminated in a conductive anode cap 'l and a conductive anode sleeve 8. The anode sleeve 8 is separated from the grid sleeve 4 by means of a second insulating sleeve 9. The operative faces of the cathode 2 and anode 6 are disposed parallel to and on opposite sides of the grid element which is terminated in the grid sleeve 4; Direct connections to the cathode, and to the heater element disposed adjacent thereto, are brought out through the base of the tube and terminated in conventional tube contact pins.

The oscillator grid circuit comprises a slotted cylindraceous inductive element I l which is inserted over the grid sleeve 4 and capacitively coupled to the shoulder of the cathode sleeve 3 through a relatively thin ring of mica. or other dielectric material l2. When in position, the slotted portions of the inductive element I l are maintained in contact with the grid sleeve 4 by the inherent resilience of the conductive element. Feedback is adjusted by varying mechanically the number of fingers ofthe slotted portions of the inductive element Il which contact the grid ring 4.

A second xed inductive element, comprising the anode circuit, includes a cylindrical conductlng member I3 to which is secured a pair of slotted cylindraceous contact portions I4, I5 which contact respectively the anode cap 'I and the anode ring member 8. A second cylindrical anode circuit portion It surrounds the rst cylindrical portion I3 and includes slotted resilient end portions I1 which engage the cathode sleeve 3. If desired, the anode circuit portions I3, I6, II may be of unitary construction.

It will be seen that the anode circuit portions I3, I6 provide an inductive circuit between the tube anode 6 and the cathode shell 3 which in turn is coupled capacitively to the cathode 2. Similarly, the anode circuit inductive elements I3, I6 are coupled inductivelyy to the grid-circuit element II since both anode and grid circuit elements are coaxial with the thermionictube I. Actually, in effect. the cathode is coupled to an intermediate point on the main tuned Ycircuit connected between the anode and the grid, and the anode-cathode and grid cathode portions of the circuit are directly coupled and carry .nearly the same radio frequency currents.

A source` of positive anode potential is connected to the cathode shell 3 .and hence to the anode through the inductive elements I'I. I5, I3, I4 and l5. The negative terminal of the anode vol-tage supply is connected to the tube cathode terminal I8. f

Output power at the resonant frequency of the oscillator circuit is vderived by means of a coupl-ng loop I9 disposed within the anode inductive elementsk I6. I3. Output leads from the coupling coil I9 are brought out through the wall of the anode element I6 through an insulating grommet Referring to Figure 2 the equivalent electrical circuit of the devicedescribed in Figure 1 includesthe tube `I having its grid terminal connected through the inductive element. I-I and the capacitive element I2 to. the external cathode sleeve 3 which is capacitively coupled to the tube cathodeelement. The anode inductive element I3,` I6, I-'I is connected intermediate the tube anode and the external` cathode shell 3. The negative terminal of the. anode voltage supply is connected directly to the tube cathode while the positive terminal is connected to the cathode sleeve 3. Output to any desired external load circuit, not shown, is provided by inductive coupling between the anode circuit I3, IG, I'I and the output coupling coil I8, Suitable grid bias isprovided by the leakage between the cathode and theexternal cathode sleeve as indicated by the resistor 2 t shown in dash lin-es. l

The oscillatorA thus described will be resonant at a particular frequency in the centimeter wave. region determined by the physical proportions of' the anode circuit elements I3, I6, I'I. The feedback will be determined by the number of inger portions of the conductive grid element I I which are in contactv with the grid sleeve 4., Extremely h-i'ghgpower output may be derived from the circuit due to the relatively heavy anode circuit components, 'lhe inherently compact proportionsprovided by the coaxially disposed tube and circuit elements greatly facilitates design of the circuit for extremely short centimeter wavelengths.Y Y i Referring to Figure 3, the tube and gridV circuit arrangements areY similar to. that describedl in Figures land 2 with the Aexception thatv an external grid leak 22 is connected between theV grid inductive element II and the resilient lingers I1 ofi the anode inductance I6 which arey in cond tact with the external cathode sleeve 3. Alternatively, the grid bias resistor 22 may be connected directly between the grid Il and the cathode terminal I8. The grid circuit feedback is adjusted, as described heretofore in Figure l, by varying the number of contact lingers of the inductive element II which are permitted to contact the grid sleeve 4.

'The anode circuit comprises means for adjusting the oscillator over a selected frequency band `without affecting substantially the inductive feedback required to provide sustained oscillations. The anode circuit includes an external cylindrical Yconductive shell I6 Which includes ,longitudinal 'slots 2.3, and which is terminated at its end remote from the thermionic tube in an apertured` plug portion 24. The apertured plug portion 2li includes a bushing 25 having a bearing arranged to receive a tuning shaft 23 which extends therethrough. The shaft 25 carries an, insulating bushing 21 which is threaded thereto. Thevbushing -2'I supports a longitudinally movable internal conductive shell Vfaiircoaxially disposed with respect to the outer Vconductive shell IE. Insulating studs 29, extending through the apertures 23 of the outer conductor shell I6', provide guides to prevent rotation of the inner conductive shell 28 as the inner shell is moved longitudinally with respect to the outer shell. The spacing between the outer sur,- face of the inner shell 28 and the inside surface of the external shell I6 should be relatively small to provide substantial capacitive coupling therebetween. A

A second internal conductive shell 3b includes cylindraceous contact means I4, I5 which engage respectively the anode contact stud 'I land anode sleeve 8 of. the thermionic tube I. The second internal conductive shell 3U is disposed coaxially with respect to the outer conductiveshell I6 and is terminated in a substantially flat end portion 3l which is in Variable capacitive relation with the adjacent end of the iirst internal conductive shell2B. The control shaft 26 is journaled into an apertured insulating plug 32 which is fixed to the inner surface of the second inner conductive shell 3D. Stop nuts 33 prevent axial movement of the control shaft 26V within the insulating plug 32. It lWill be seen that rotation of the control shaft 25 will provide longitudinal adjustment of the rst inner conductive shell 28, and hence provide variable capacitive coupling between the adjacent surfaces ofl the inner conductiveshells 28, 30,

The anode circuit may be operated at its fundamental resonance or atea predetermined parasitic frequency, determined by the desired operating frequency. g K

Anode voltage is applied through a radio frequency choke c-oil 34 and a quarter Wave line 35 to the end of the spring contact member I5 where i-t is attached to the adjacent-end of the. second inner `conductive shell 3l).

Figure 4 illustrates schematically the equivalent circuit. of the device described in/Figure 3. It vwill be seen that the tube Ik includes a fixed grid inductance II which is capacitively coupled through the capacitor I2 to the external cathode shell 3. The leakage path betweenfthe cathode and the external cathode shell 3 is indicated by the resistor 2I shown in dash lines. The grid resistor 22may be connected as shown between the grid and the cathode shell 3- or it may be connected directly between the grid and cathode tube n ductive element comprising the second inner conductive shell 30 which is in inductive relation to the outer cylindrical conductive shell I B. The inductor 30 is capacitively coupled to the inductor 28 through the variable capacitor described heretofore. The remaining terminal of the inductor 28 is capacitively coupled to the conductor I6 through the fixed capacity provided between the surfaces of the two inductive elements. The remaining terminal of the outer inductor I 6 is connected to the cathode sleeve 3. Anode potential is supplied through the radio frequency -choke coil 34 and the quarter wave conductor 35. Centimeter wave output energymay be derived from a coupling coil I9 inductively ooupledto any desired point in the anode circuit. The output winding I9 has been omitted in the device described in Figure3 to simplify the illustration thereof. It should be understood that output energy may be derived in any other manner known in the art.

Referring to Figure 5, the tube I includes a fixed inductive grid element 4l having a plurality of conductive fingers disposed in contact with the grid sleeve 4. The grid inductive element 4I is coupled capacitively to a cylindrical shield 42 which substantially surrounds the tube and all high frequency circuit portions thereof. The capacitive coupling between the grid inductive elcment 4| and the cylindrical shield 42 is provided by an enlarged base bracket portion of the inductive element 4I which is closely spaced with respect to the cylindrical shield 42. Insulated bushings 43 or insulated washers, separate these elements from the mounting screws which support the inductive element 4|; The outer cylindri-cal shield 42 includes spring contact members 44 which engage the cathode shell 3 of the tube I. A grid resistor 22 is connected between the grid inductive element 4| and the tube cathode terminal I8.

The anode circuit comprises a relatively heavy buss bar 45, having contact portions I4, I5 connected thereto in contact respectively with the anode cap 'I and anode sleeve 8 of the thermionic tube I. The end of the anode buss bar 45 remote from the anode terminals is terminated in a fiat plate 46 whi-ch is separated by a layer of mica or other insulating material 4'| from the closed end portion 48 of the external cylindrical shield 42 adjacent the contact fingers 44 which engage the cathode sleeve 3. The capacity between the conductive elements 46, 48 provides ample capacitive coupling between the anode and cathode circuit elements. The positive anode potential source is connected, through a suitable isolating resistor 49, to a terminal -50 which is connected to the capacitive plate 46 and hence to the anode buss bar 45.

The anode circuit also includes a variable capacitive element comprising a resilient rst capacitive plate 5I supported by the anode bus-s bar 45 at a point adjacent the anode contact I4. A second capacitive plate 52 is resiliently supported by a spider 53 to the edges of an aperture in the wall of the cylindrical shield 42. The second capacitive plate 52 is coupled mechanically to the diaphragm 54 of a vibrating element such as, for example, a dynamic loudspeaker unit 55.

A control knob '56, secured to a control shaft 5l of insulating material, is threaded through a bushing 58 in the side wall of the cylindrical shield 42 diametrically opposite from the loudspeaker unit 55. Rotation of the control knob 55 provides manual adjustment of the relative spacing of the capacitive plates 5|, 52 for controlling the shunt capacitance in the anode circuit. Actuation of the loudspeaker unit 55 by any suitable source of modulating currents thereby provides frequency modulation of the oscillator output at the mean carrier frequency selected by the preliminary adjustment of the -control knob 56.

Figure 6 illustrates schematically the equivalent electrical circuit of the device described in Figure 5. .It will be seen that all high potential radio frequency circuits are enclosed substantially within the shield 42 and that tuning is provided by the shunt capacitance 5I, 52 connected between the anode of the tube I and the cathode sleeve 3. Output may be derived from an output coupling coil I9 coupled in any known manner to the lanodebuss bar 45. It should be underst-ood that the embodiment of the invention illustrated in Figures 5 and 6 may be operated at substantially lower radio frequencies than could be readily provided in the devices previously described in Figures 1 and 3. Adjustment of the grid circuit may beprovided in the same general manner as described heretofore in the other embodiments of the invention.

The frequency-modulated oscillator thus described may be employed in any manner known in the art such as, for example, the generation of distinctive radio beacon signals, the jamming of other radio signal transmission, the generation of signals for the purpose of distance determination or object location, or as a sweep oscillator for receiver selectivity observation.

Thus the invention described comprises three embodiments of a centimeter wave oscillator employing lixed inductive coupling between anode and grid portions of the circuit to sustain oscillations at predetermined super-high frequencies.

I claim as my invention:

1. An ultra-high-frequency oscillator including a thermionic tube having at least an anode, a cathode and a control electrode, means including first inductive means and rst capacitive means connected between said control electrode and said cathode, means including second inductive means and vsaid capacitive means connected between said anode and said cathode, said rst and said second inductive means being mutually coupled and portions thereof being disposed substantially coaxially with said tube to provide regenerative feedback to sustain oscillations in said circuit.

2. An ultra-high-frequency oscillator including a thermionic tube having at least an anode, a cathode and a control electrode, means comprising a rst cylindraceous inductive element having a plurality of longitudinal slots in one end thereof, said slotted end being slidably connected to said control electrode and another portion of said element being capacitively coupled to said cathode, and means comprising a second inductive element inductively coupled to said cylindraceous element and concentric therewith to provide inductive feedback and having separate portions thereof slidably connected to said anode and capacitively coupled to said cathode, respectively.

3. Apparatus as claimed in claim 1 including variable capacitive means coupled between said anode and said cathode for adjusting the frequency of said oscillator.

4. Apparatus as claimed in claim 1 including motor driven variable capacitive means coupled between said anode and said cathode for adjusting the frequency of said oscillator.

5. Apparatus as claimed in claim 1 including separate motor driven and manually operable variable capacitive means coupled between said anode and said cathode for adjusting the frequency of said oscillator.

6. Apparatus as claimed in claim 2 characterized in that said second inductive element comprises three coaxially disposed capacitively coupled ,conductive means, and means coupled to one of said conductive means for adjusting the position of said one of said .conductive means to vary substantially the capacitive coupling between only two of said three conductive means.

7. Apparatus as claimed in claim 2 including cylindrical conductive shielding means substantially surrounding said tube and sai-d inductive and capacitive elements, said shielding means being open at one end for access to said oscillator and being capacitively coupled at the remaining end to said cathode and said second inductive element.

8. An ultra-high-frequency oscillator including a thermionic tube having at least an anode, a cathode and a control electrode, means comprising a first cylindraceous inductive element having a plurality of longitudinal slots in one end thereof, said slotted end being slidably connected to said control electrode and another portion of said element being coupled capacitively to said cathode, and means comprising a second cylind-raceous inductive element substantially surrounding and coaxial with said tube and concentric with said first element providing feedback coupling to said first inductive element and having separate portions thereof slidably connected 8 to said anode and capacitively coupled to said cathode,respectively. u

9. In combination, an ultra-high-frequency thermionic discharge tubehaving a plurality of tube electrode terminals and an inductor comprising a cylindraceous conductive element having one end capacitively coupled t0 one of said tube electrode terminals and said element being longitudinally slotted for a substantial portion of its length from its other end to provide a plurality of longitudinally extending portions effectively comprising a plurality of parallel connected inductances engaging another of said tube electrode terminals, said inductor being disposed coaxially with said tube.

10. Apparatus as claimed in claim 9 wherein predetermined ones of said extending portions of said inductor are spaced from said last-mentioned tube electrodev terminal.

` ALFRED H. TURNER.

REFERENCES CITED The following'refer-ences are of record in the file of this patent:

' UNITED STATES PATENTS Date 

